The present invention generally relates to a system for improving the total thickness variation across a surface of a bulk semiconductor wafer and, in particular, relates to one such system having means for measuring the initial total thickness variation of the surface of the bulk semiconductor wafer.
As the size of semiconductor devices decreases and the requirements for more devices to be formed on a given wafer increases, the density requirements of the semiconductor device manufacturers increases. As a result, what used to be acceptable thickness variations across tie surface of a semiconductor wafer is rapidly becoming unacceptable since, as the individual devices become smaller, the impact on each surface variation becomes more significant, i.e., each variation in the surface of a semiconductor may now catastrophically affect a plurality of devices and thus reduce the yield from the wafer more significantly. Hence, one of the factors limiting the chip or circuit density available to the semiconductor industry is the total thickness variation across the surface of the semiconductor wafer.
Currently, a bulk semiconductor wafer is cut, typically be use of a diamond saw blade device, from a semiconductor boule that is grown with a predetermined crystalline orientation. Once sawed, the bulk semiconductor wafer is subjected to numerous grinding and polishing processes with a combination of coarse and fine abrasives to remove damage induce by the sawing device. The wafer surface is subsequently treated with a combination of very fine abrasives and reactive liquids to remove the damage induced by the coarse grinding and polishing processing. The grinding and polishing operations are intended to uniformly remove material from every location on the wafer surface simultaneously. Further, to achieve economical advantages in the production processing of bulk semiconductor wafers, such operations are typically conducted on several wafers at a time, generally referred to as batch operation.
The general result of such batch processing is that individual bulk semiconductor wafers produced by this method may have surfaces that deviate from planarity by about 5 micrometers. Such deviation may be increased when the wafer is constrained, or mounted, for subsequent processing, by a planar vacuum mounting device, such as a vacuum chuck. This non-planarity creates significant problems in advanced device fabrication processes employing microlithographic exposure tools which typically have a limited depth of focus. Further, the finished surfaces of such wafers may conceal small, but significant amounts of subsurface crystalline damage resulting from the grinding and polishing operations.
Typically, with current minimum circuit pattern sizes between 0.5 micrometers and 1 micrometer, lithographic systems have a depth of field of about 0.5 micrometers. It is anticipated that next generation devices will have pattern sizes less than 0.5 micrometers and the depth of field of optical lithographic systems will be about 0.1 micrometers. Hence, the variation in the surface thickness should be such that features of this size can be formed without encountering a thickness variation that disturbs or prevents such a feature from being fabricated. However, it is quite clear that in order to ensure that any area on the wafer selected for an exposure field is flat, the entire surface of the wafer must be worked to that flatness.
Consequently, a system for improving the total thickness variation of a surface of a bulk semiconductor wafer is greatly needed and desired in the semiconductor industry.
Accordingly, it is one object of the present invention to provide a system for improving the total thickness variation of the surface of a bulk semiconductor wafer that substantially overcomes the above-recited drawbacks of conventional systems.
This object is accomplished, at least in part, by a system for improving the total thickness variation of a surface of a bulk semiconductor wafer that includes means for measuring the initial total thickness variation of a surface to be treated and means for selectively removing material from the surface of the wafer in accordance with the measured initial total thickness variation such that the final total thickness variation is minimized.
Other objects and advantages will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.